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Black locust is native to the United States, though the extent of its original range is not accurately known. It is thought that black locust was originally found in 2 regions. The eastern region was centered in the Appalachian Mountains and ranged from central Pennsylvania and southern Ohio south to northeastern Alabama, northern Georgia, and northwestern South Carolina. The western region included the Ozark Plateau of southern Missouri, northern Arkansas, and northeastern Oklahoma and the Ouachita Mountains of central Arkansas and southeastern Oklahoma. It is thought that outlying native populations existed in southern Indiana and Illinois, Kentucky, Alabama, and Georgia (review by [167]). The US Geological Survey provides a distributional map of black locust's native range in North America.
Black locust has been widely planted and frequently escapes cultivation ([53,123,124,128,190,215,325,360], review by [167]). As of 2009, it occurred throughout the conterminous United States and a number of Canadian provinces. Plants Database provides a map of black locust's distribution in North America. Black locust also occurs in parts of South America, Europe, Asia, Africa, and Australia (review by [340]).
Fuels: Outside its native range, black locust may alter fuels in 2 ways that influence FIRE REGIMES. First, black locust may increase the extent and relative density of forest compared to native plant communities. This change in structure was noted specifically in open habitats in the Northeast and mid-Atlantic states [83,273], and is likely of concern in other open habitats where black locust establishes. Second, black locust may produce a litter layer that differs from that produced by native vegetation. Natural and planted stands of 21- to 35-year-old black locust in Illinois, Indiana, and Ohio contained 10,200 dry-weight pounds of litter/acre [9]. On the Albany Pine Bush Preserve in New York, black locust stands had a 2-fold greater litterfall mass compared to native vegetation [272]. Black locust litter decomposes quickly [9,272] and is generally moist, which may differ from the litter characteristics of native vegetation [90]. One author suggests that black locust stands in pitch pine-scrub oak forests have higher live:dead fuel ratios and fuel moisture than native vegetation, slowing surface fire rate-of-spread and consequently altering FIRE REGIMES [90]. It is therefore unclear whether the quantity of litter represents an increased fuel load or the characteristics of the litter represent a decreased fuel hazard.
FIRE REGIMES: Vegetation in the native range of black locust was historically maintained by a variety of disturbances, including fire (see Successional Status for more information on disturbances). Black locust is well adapted to disturbances such as fire (see FIRE ADAPTATIONS AND PLANT RESPONSE TO FIRE), and fires in these ecosystems likely played a historical role in black locust establishment.
The current distribution of black locust includes ecosystems that historically experienced both frequent and infrequent fires of various severities. The impacts of black locust on these FIRE REGIMES is largely unknown, though there is some concern that black locust may alter FIRE REGIMES in fire-adapted ecosystems like the pitch pine-scrub oak forests in the Northeast. In these systems, black locust is less flammable than the vegetation it is replacing [83]. Some managers even consider black locust "nonflammable" [81]. In a series of laboratory trials, black locust had significantly lower combustion rates and total heat release than pitch pine (P<0.0001) [83]. Black locust litter lies flat on the forest floor and tends to stay relatively damp due to the closed-canopy conditions under dense stands. High live:dead fuel ratios and fuel moistures develop under these stands, which may slow surface fires [90]. These characteristics lead a number of authors to suggest that fire intensity, fire-return intervals, and FIRE REGIMES may be altered in pitch pine-scrub oak forests where black locust is established [81,83,90]. In pitch pine sites, black locust may lengthen the fire-return interval to an unsustainable level, with pitch pine eventually being shaded out along with native fire-adapted understory plants [81]. In this and other ecosystems, black locust also facilitates the establishment of nonnative grasses and other invasive species [82,90,133,252], which might further alter FIRE REGIMES.
See the Fire Regime Table for further information on FIRE REGIMES of vegetation communities in which black locust may occur in its native and nonnative ranges. Find further fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find FIRE REGIMES".
Black locust seeds require scarification ([325], reviews by [167,181]) and bare mineral soil ([164,216], review by [314]) for successful germination. Though one source cites germination rates as high as 68% in its native range [325], most sources suggest that seed germination is low (review by [131]) due to high seed coat impermeability ([252], review by [226]) and shade intolerance [164,252]. Direct-seeded black locust on limestone and acid-shale sites in Ohio had low germination rates, ranging from 3% to 17%. Survival of these germinants ranged from 23% to 78% [202]. Fifteen to 33 days after planting in a greenhouse, fall-collected black locust seeds from New Haven, Connecticut, exhibited 45% germination. The addition of various salt concentrations delayed and slightly lowered percent germination [19].
In greenhouse trials, black locust seeds germinated uniformly over a 5-week period [87].
The following section examines site characteristics such as general types of sites, elevation, soil characteristics, topography, and climate in black locust's native and nonnative ranges.
Native range:
General In its native range, black locust occurs in a wide range of forest communities (see Habitat types and plant communities for specific community associations), as well as a variety of disturbed sites such as old fields ([169,225,332], reviews by [167,314]) and logged areas [15,46,184,220,228,288,317]. It generally occurs at low density within the forest interior but establishes well in forest openings, edges [216], and other early-successional habitats. See Successional Status for more information.
Elevation: A silvics guide states that in its native range, black locust thrives best on moist slopes of the eastern mountains below 3,400 feet (1,040 m) (review by [167]). It occurs below 300 feet (90 m) in parts of Kentucky [41] and Tennessee [350] and above 4,000 feet (1,200 m) in Great Smoky Mountains National Park ([45], review by [167]).
Soils: Black locust occurs in a variety of soil types within its native range. Numerous sources associate black locust with limestone ([39,41,121,172,268,311], reviews by [167,312]), but it is also associated with sandstone [2], chert [268], and mica-gneiss substrates [211]. Soils tend to be loams ([129], reviews by [167])) or sandy loams [246]. Other soil characteristics associated with black locust include "rich" ([41], reviews by [167,312]), deep ([41], review by [312]), well-drained ([2,38,129], review by [312]), and moist ([78], review by [167]) conditions.
Black locust may not grow well on very sandy, very acid, or wet soils (review by [312]). It is sensitive to soil conditions that produce either minimal or excessive aeration and drainage (reviews by [66,167]). Black locust growth is limited by water-logged soils or soil compaction (review by [66]).
In its native range, black locust tolerates a range of soil acidities; a pH of 4.6 to 8.2 is listed as "acceptable" in 2 reviews [26,167]. Soil at a site within its native range in the Nantahala Mountains of western North Carolina had a pH of 4.7 [211]. In the Great Smoky Mountains of Tennessee and North Carolina, black locust was found in soils with a pH of 5 [47].
Topography: Black locust is often found on slope forests within its native range ([1,2,29,211,350], review by [167]). In the Monongahela National Forest in central West Virginia, black locust occurred on slopes of 45% to 55% [2]. In the Nantahala Mountains of western North Carolina, it occurred on a 21.6° slope [211]. Black locust has been found on northwestern slopes in eastern West Virginia [1] and southerly slopes in North Carolina and Tennessee [350].
Black locust is also found on valley floors [1], bottomlands [38], floodplains [77], ridges [350], rolling uplands [41], and loess hills [40,77].
Black locust occurs in a variety of forest types in the Black and Craggy Mountains of western North Carolina, though at very low densities [222].
Relative density of black locust in xeric to mesic oak forests [222]
Forest type
Dominant species
Forest characteristics
Percent density of all trees
Mixed-oak
mixed-oaks, yellow-poplar, red maple, American beech, hickories
2,500-3,400 ft, moderately sheltered low ridges, flats and valleys, dry-mesic, moderate nutrients
1.3
White oak
white oak, American beech, red maple
well-drained valley flats and terraces,
dry-mesic, nutrient rich, high pH
1.6
Scarlet oak
scarlet oak, red maple, sourwood
<3,400 ft, south- and west-facing ridges, slopes, and flats, dry-mesic, intermediate in nutrients and pH
2.3
Northern red oak, chestnut oak, yellow-poplar
northern red oak, chestnut oak, yellow- poplar, red maple
3,200-4,000 ft, open slopes of all aspects, intermediate nutrients and pH
1.5
Chestnut oak
chestnut oak, scarlet oak, black oak, northern red oak, pignut hickory, red maple, black tupelo
3,000-4,500 ft, south- and southwest-facing slopes and narrow ridges of most aspects, xeric, nutrient poor
1.6
Red oak
northern red oak, red maple, sweet birch, American beech, eastern hemlock
4,000-5,000 ft, middle and upper slopes, ridgetops, intermediate in moisture and nutrients
0.5
Relative density of black locust in mesic to wet forests [222]
Forest type
Dominant species
Forest characteristics
Percent density of all trees
Cove hardwoods
sugar maple, basswood, American beech, yellow buckeye (Aesculus flava), yellow birch
<5,000 ft, low, predominantly north-facing slopes, coves, and sheltered slopes, wet-mesic, high nutrients and pH
1.3
Northern red oak
northern red oak, yellow-poplar, sugar maple, eastern hemlock, American beech
slopes adjacent to cove forests, slightly lower moisture, nutrients and pH compared to cove forests
0.7
Alluvial
American sycamore, yellow birch, eastern hemlock, red maple
floodplains and terraces of large streams, mesic, moderate nutrients
0.2
Hemlock hardwoods
yellow birch, eastern hemlock, red maple, sweet birch, witch-hazel (Hamamelis virginiana)
slopes and hollows adjacent to mesic red oak forests, upstream from alluvial forests, 1st- and 2nd-order stream flats and in ravines, mesic, low nutrients and pH
0.4
Climate: Climate conditions in black locust's native range are humid, though it has been successfully introduced into many parts of the world where climate conditions vary widely from those listed below (review by [167]).
Climate conditions for black locust's native range (review by [167])
Minimum Maximum January normal daily temperatures -7 to 2 °C 2 to 13 °C August normal daily temperatures 13 to 21 °C 27 to 32 °C Mean length of average frost-free period 150 days 210 days Normal annual total precipitation 1,020 mm 1,830 mm Mean annual total snowfall 5 cm 152 cmNonnative range:
General Outside of its native range, black locust thrives in disturbed ([12,91,210,231,237,272], review by [26]) or "waste" areas [31,329]. Specific examples of disturbed areas include roadsides ([53,85,113,128,153,215,329], reviews by [26,72]), railroad right-of-ways [144], constructed wetland edges [200], disturbed hammock margins [360], man-made sandflats [224], and channel levees [296].
Many disturbed black locust sites are also associated with human habitation and agricultural operations. Black locust occurs in fencerows and hedgerows ([85,113,124,143,161,325,329,341], review by [72]), abandoned agricultural fields [60,80,97,160,165,210,237,327,329,332] and pastures ([113,128,313], review by [72]), and near old home or farm sites [53,152,153,156,192,198,231,231,325,341].
Black locust spreads from disturbed sites into areas such as forests ([58,113,116,161,232,329], forest edges [124,165], reviews by [71,72]), woodlands [128], woodland openings [165], thickets [128,232], or prairies and other grasslands ([310], review by [72,173,289]). See Habitat types and plant communities for descriptions of plant communities where black locust occurs outside its native range.
Black locust often establishes in riparian areas such as stream- and riverbanks and floodplain forests throughout its nonnative range, including locations in the Southeast [77,294], Northeast [12,116,200,224,254,332], Great Lakes [58], Northern Great Plains [128], Northern and Central Rockies [91,192] Northwest [17,156,198,259], Southwest (review by [307]), and California ([73,94,111,152,153,197,279,296], reviews by [26,95,290]).
Elevation: In its nonnative range, black locust is found at a wide range of elevations. The following table demonstrates that black locust may occur anywhere from 30 to 6,500 feet (10-2,000 m) in its nonnative range.
Elevation (feet) Location 30-350 southeastern Louisiana [77] 80-240 central Maryland [161] 160-6,300 California ([153], review by [26]) 1,000 southwestern Wisconsin [67] 3,115-3,135 Grand Canyon National Park, Arizona (review by [307]) 3,770 Las Cruces, New Mexico [185] 4,450 midwestern Himalaya of India [182] 4,500-5,500 Colorado [143,341] 4,920-7,545 southwestern New Mexico [22] 5,000-6,200 Sierra Nevada, California [295] 6,500 New Mexico (review by [302])Soils: In its nonnative range, black locust is found in a wider range of soil conditions than within its native range. An association with limestone or calcareous soil is noted in the Southwest [325], the Northeast, and Canada [113]. In contrast to its native range, a strong association with sandy soils is found in the Northern Great Plains [303], north-central Texas [85], Illinois [5,133], the Northeast [236], Maryland [254], California ([296], review by [131]), and Hungary ([218], review by [181]). Many of these locations are either sand dunes or sand prairies [5,133], or stream or river deposits [236,254,296]. Black locust was found on fertile loam near the Sacramento River in California [197], Richfield silty loam in the high plains regions of the Oklahoma panhandle [42], silty-clay loam in eastern Nebraska [301], well-drained loams in eastern Washington and northern Idaho [32], and silty or sandy loams with loose structure in Hungary (review by [181]). Clayey soils were listed as "inappropriate" in Hungary (review by [181]), and sandy or constantly wet soils were not conducive to growth in eastern Washington and northern Idaho [32].
A preference for moist sites is noted in the Northern Great Plains [313], northern United States and southern Canada [113], and Hungary (review by [181]). Black locust's deep rooting ability may allow it to grow in locations much drier than in its native range (review by [167]). Black locust was one of the most abundant trees establishing in dense stands on "poor", dry soils on man-made sandflats along the Hudson River in eastern New York [224]. Several sources suggest that as in its native range, black locust does best on well-drained sites ([313,325], review by [204]). One source states that black locust prefers deep soils in the Southwest [325], though another states that it may grow well on shallow soils in the Northeast (review by [204]). Black locust is found on sites that range from low ([224], review by [204]) to intermediate [236] and high [197] soil fertility in its nonnative range. The ability of black locust to establish and persist in areas with low soil nutrient levels (like the pitch pine-scrub oak forest type in New York [272] or dry grasslands in Europe ([99], review by [340])) is highly problematic to land managers (see Impacts).
Black locust has been planted on soils with a wide range of pH and tolerates extremely acidic soils, particularly in strip-mine reclamation sites [3]. For example, 21% of 1- to 2-year-old black locust seedlings survived soil pH as low as 2.85 on acid strip-mine spoil in southwest Indiana, though higher survival was observed when lime was added to raise the pH [151]. One biofuel plantation site in Las Cruces, New Mexico, had a soil pH of 7.9 [185].
Topography: Black locust is commonly found on slopes across its native and nonnative ranges. In southwestern Michigan, it occurred on the south slope of a large moraine [189]. In Ohio, black locust was most abundant on dry hillsides [31]. In California, it was locally abundant on canyon slopes [153]. In the Palouse prairie region of eastern Washington and northern Idaho, black locust occurred on hills and slopes too steep to plow [32].
Climate: Black locust is highly susceptible to frost and cold weather damage (reviews by [167,312]), which may limit expansion of its range. Black locusts planted in Ontario were limited by hard winter frosts that killed new growth [16]. Frost is listed as the most important abiotic threat to black locust in Hungary; it may damage shoots and decrease growth, leading to dwarfed trees over time (review by [181]).
Few authors report climate data for areas where black locust has either been planted or established outside its native range. Plantations of black locust were started in Las Cruces, New Mexico, an area with a minimum winter temperature of 18.1 °F (-7.7 °C) and a maximum summer temperature of 100.9 °F (38.3 °C) [185]. Near Albany, New York, black locust established in a region with average temperatures of 21 °F (-6 °C) in January and 72 °F (22 °C) in June [272]. Black locust also established in western Maine, where January temperatures ranged from 4.5 to 27.0 °F (-15.3 to -2.8 °C) and July temperatures ranged from 54.7 to 80.8 °F (12.6-27.1 °C) [12].
Black locust grows well in the Palouse prairie region of eastern Washington and northern Idaho, where average annual high and low temperatures for Moscow, Idaho, are 58.1 °F (14.5 °C) and 35.8 °F (2.1 °C) respectively, and average annual high and low temperatures for Colfax, Washington, are 59.9 °F (15.5 °C) and 36.5 °F (2.5 °C) respectively. This area infrequently experiences long periods of subzero temperatures in the winter [32].
Low precipitation may also limit black locust persistence or range expansion. Only 8% of black locust survived that were planted in the sagebrush desert of south-central Oregon, an area receiving less than 10 inches (250 mm) of annual precipitation (review by [186]). For rehabilitation in Utah, a reclamation handbook notes that black locust grows as a shrub at temperate climate sites that receive more than 12 inches (305 mm) of annual precipitation, and as a small tree at sites receiving more than 15 inches (380 mm) of annual precipitation (review by [257]). Black locust was found in southwestern Wisconsin, an area with an average annual precipitation of 30.6 inches (777.2 mm) [67], as well as in western Maine, where average annual precipitation was 44 inches (1,116 mm) [12].
Though often considered poisonous to livestock, black locust is grown in some areas specifically as livestock forage. Black locust provides food and structural habitat for a variety of wildlife species.
Palatability and/or nutritional value: Numerous accounts describe parts of the black locust as poisonous to livestock including mules (review by [69]), horses ([136,313], review by [69]), cattle [136,303,313], and domestic sheep ([313], review by [69]) due to the presence of the poison robotin [136]. Poisonous plant parts include the roots [303], young shoots ([136,303,313], review by [98]), seeds [85,153,190,258,313], twigs [113], leaves [85,153,258], and bark ([85,113,136,153,258,313], review by [98]). In some cases, poisoning may be fatal to livestock ([136,153], review by [69]), though one author asserts that fatality from poisoning is rare [313]. In livestock, symptoms of black locust poisoning may include reduced hearing, stupor, vomiting, and purging (review by [98]).
Despite the potential for black locust poisoning and its classification in one guidebook as worthless to poor forage for livestock (review by [69]), black locust is used as livestock feed in parts of its introduced range. It is grown to feed domestic goats in northern Pakistan [10], domestic sheep and goats in New Zealand [193,249], and general livestock in Bulgaria and Korea (review by [181]). In Mendocino County, California, chickens were observed eating black locust seeds, and horses ate the leaves sparingly [57]. In North Carolina, domestic goats and cattle defoliated black locust shoots in an abandoned orchard. The level of browsing was substantial enough to kill all black locust after 4 years of browsing [206].
Black locust is a food item for many wildlife species. White-tailed deer heavily browse black locust in North Carolina, [79], Georgia [141], and Arkansas (review by [69]), though one study found a lack of white-tailed deer herbivory on black locust in Maryland and West Virginia [139]. Mule deer browse black locust in Washington [50], California ([199], review by [132]), and New Mexico (review by [191]). Rabbits browse on stems ([188], review by [263]). Ruffed grouse eat black locust leaves [348]. Squirrels ([313], reviews by [69,312]), doves [320], California quail (review by [132]), northern bobwhite ([110,138,170,275], review by [312]), chukar (review by [132]), pheasants ([303], review by [312]), ruffed grouse [348], and other game birds ([303], review by [312]) eat black locust seeds.
Invertebrate species also consume black locust. Freshly fallen black locust leaves were palatable to millipedes in laboratory studies [207]. Black locust was a host to the Lepidopteran species the silver-spotted skipper and the three-staff underwing in the southeastern United States [320], and it is widely visited by bees for its nectar throughout its native and nonnative ranges ([313], review by [167]).
Nutritional content: Black locust seeds are high in crude protein ([253,258], review by [312]), phosphorus ([253], review by [312]), and crude fats and low in calcium (review by [312]). Black locust leaves had the highest nitrogen content of any tree tested in a North Carolina mixed-oak-hardwood forest [75]. Five- to 10-year-old black locust in a western North Carolina mixed-oak and cove hardwood forest had significantly higher leaf nitrogen than the other 7 dominant species tested (P=0.0001). Along with yellow-poplar, black locust also had higher leaf potassium and phosphorus compared to other species (P=0.0001) [103].
Humans: Black locust is poisonous to humans [85,153,313]. In some cases, poisoning may be fatal [153]. Symptoms of black locust poisoning include dilated pupils, feeble pulse, severe vomiting, and a death-like pallor [136]. Humans may get dermatitis from exposure to black locust wood [3].
Some people eat fried or cooked black locust flowers [303,313]. Tea can be made from the flowers [313].
Cover value: Black locust is an important cover species for wildlife (review by [167]), providing nesting, roosting, and thermal cover. The persistent nature of black locust stems after plant death makes it an important resource for cavity-dependent wildlife species [248]. A disproportionate number of snags were identified as black locust in a Maryland old-growth forest remnant [88], a 24- to 64-year-old yellow-poplar-red maple stands in southeast Ohio [92], and second- and old-growth mixed-hardwood forests in eastern Kentucky [220]. Compared to surrounding forest, a disproportionate number of cavities were found in black locust trees in mixed-hardwood [177] and oak-hickory [48] forests in West Virginia.
Black locust cavities are used for nesting and roosting by bats and birds. Black locust cavities were used as maternity roosts for long-eared bats in West Virginia [228,248] and the endangered Indiana bat in the Champlain Valley [336], and as day roosts for male northern bats in West Virginia [115]. In its native range, black locust provides nesting cavities for birds such as the hairy woodpecker [65], downy woodpecker [65], northern flicker [65,219] and red-bellied woodpecker [219]. In Kentucky, eastern screech-owls roosted in black locust cavities in the winter [96].
Black locust cover is also important to birds. Black locust was positively associated with red-eyed vireo habitat in southwestern Virginia [163] and rufous-sided towhee habitat in Maryland [119]. In a mixture of small deciduous woodlots and thickets interspersed with old fields in Kentucky, adult and juvenile eastern screech-owls used black locust stands for roosting in the postfledging period [18].
Outside of the native range of black locust, birds that nest in black locust foliage include the black-billed magpie, western kingbird, Baltimore oriole [28], and Swainson's hawk in eastern Washington [14,28], the long-eared owl [212] and loggerhead shrike in Idaho [358], and the dickcissel in central Oklahoma [247]. Near Cape Cod, Massachusetts, black locust stands provided suitable cover for northern bobwhite and American woodcock [275]. In south-central Kansas, 62 breeding bird species were detected in shelterbelts containing black locust [287], and black locust was highly recommended for planting as wildlife habitat in the Northern Great Plains region (review by [148]).
Black locust occurring in small (0.52 acre (0.21 ha)) to large (8.92 acre (3.61 ha)) patches in the Palouse prairie region of eastern Washington and northern Idaho provided winter thermal, loafing, and hiding cover for 7 mammal species (moose, white-tail deer, coyote, North American porcupine, striped skunk, house cat, and mountain cottontail), 23 avian species (including gray partridge, ring-necked pheasant, red-tailed hawk, rough-legged hawk, great-horned owl, and short-eared owl), and 1 reptile (garter snake) [32].
The wood of black locust is heavy, strong, and durable [85,113,156,165,311] and shrinks little upon drying [303]. Its strength is due to high lignin content [142]. Consequently, the wood of black locust is valuable for a variety of uses, such as fenceposts [3,31,97,113,165,311,313,344], railroad ties ([165,313], review by [167]), insulator pins ([3], review by [167]), mine timbers ([3], review by [167]), shipbuilding ([3,311], review by [167]), furniture [3], handles [165], barrel staves (review by [145]), boxes and crates, pulp, and fuelwood (review by [167]).
Black locust has been widely planted for windbreaks and shelterbelts ([97,277], review by [167]), as woody biomass for energy production [23], and as a street or ornamental tree ([97], reviews by [145,167]). It has also been widely planted for honey production ([344], reviews by [145,167,181]). One author claims that black locust plantations provide the basis for Hungary's commercial honey industry (review by [181]).
The nitrogen-fixing abilities of black locust have prompted its planting in nurseries and plantations to assist the growth of other desired trees ([59], review by [167]). Black walnut [286], southern catalpa (Catalpa bignoides) [114], and hardwoods in Indiana [49] have shown improved growth when planted with black locust. In Canada, black walnuts interplanted with black locust had higher foliar nitrogen content than those not planted with black locust [326]. However, the wide-spreading crown and prolific root sprouts of black locust may suppress or kill slow-developing interplanted tree seedlings in some plantation settings [256].
Black locust was once a favored tree for restoration or rehabilitation because its extensive root system holds and stabilizes the soil surface, it sprouts vigorously and prolifically, it increases soil fertility through nitrogen fixation [180], and it forms a leaf litter that protects the soil [9,180,291]. Its main use has been in the rehabilitation of former surface mine sites ([3,16,51,113,159,238,267], reviews by [167,204]) and for erosion control ([31,97,121,176,313], review by [157]), but it is also used to rehabilitate contaminated soils [52,267], depleted soils [27], gravel pits [113], and logged areas [267] and to stabilize railroad embankments (review by [145]) and highway edges (review by [302]).
In both its native and nonnative range in North America, mortality is caused by insects and disease ([117,281,303], review by [167]). Black locust is highly susceptible to witches' broom disease caused by the virus Chlorogenus robiniae (review by [167]), as well as fungal diseases leading to heart rot ([117], review by [167]). In South Carolina hardwood stands, 13.5 % of poletimber-sized and 30.4 % of sawtimber-sized black locust had hardwood cankers [4]. In the Great Plains, black locust was susceptible to stem decay fungi; about 25% of the 40-year-old windbreak black locust planted in Oklahoma was infected with stem decay fungi (review by [274]).
In the United States and Canada, the most serious insect threat to black locust is the locust borer ([113], reviews by [26,167]). This species is often the cause of rapid population declines in plantation settings in black locust's native [27,121,281] and nonnative ranges ([36], review by [86]), and a major reason that planting black locust has fallen out of favor in the United States [121]. An Element Stewardship Abstract for black locust suggests that rapidly growing trees more than 10 years old are not usually attacked by locust borer (review by [66]). However, another author states that locust borers require the furrowed bark of older trees for egg laying. Consequently, young trees with smooth bark are not impacted [365]. On mined sites in Illinois, planted black locust declines attributed to the locust borer were seen within 15 years of planting, and after 60 years, all black locust were dead [281]. In a dense, early-successional black locust stand in western North Carolina, 21% of the black locust stems were standing dead, and 18% had greater than 50% crown dieback, primarily from damage by the locust borer [234]. Locust borer infestations not only cause mortality, but may inhibit growth ([121], review by [167]) and reproduction [59]. Locust borer infestations may be higher when trees are stressed due to poor soils ([27], review by [167]) or dense stand conditions [234].
Other potential insect pests in the native range of black locust include locust leaf miners ([117,365], review by [167]) and the locust twig borer (review by [167]). Outside of its native range in the Northern Great Plains, black locust is susceptible to the carpenterworm and ash and honey-locust plant bugs (review by [86]). Roots of the black locust are parasitized by root-knot and root-lesion nematodes in nurseries in the Northern Great Plains ([284], review by [274]).
A lack of mortality-inducing insects or diseases outside of North America is one reason black locust plantations remain popular throughout the world. In 1980, there were approximately 2.5 million acres (1 million ha) of planted black locust across the globe (review by [181]).
Within its native range, black locust generally flowers from April to June ([165,261,311,356], review by [167]), though one source states it may flower as early as February in the Southeast [97].
In its nonnative range, flowering occurs mostly from May to June in the Pacific Northwest [156], California [239], the Southwest [325], Northeast and Canada [123], and Great Plains [128,313]. Earlier flowering occurs from March to May in north-central Texas [85], while later flowering occurs in some parts of New England, extending into July [292]. In the uplands of the Adirondacks, flowering generally occurs only in June [190].
Fruit begins ripening as early as July in the Carolinas [261] or August in Arkansas [165], and ripening extends into November [165,261]. In the Southwest, fruit ripens from September to October [325]. Black locust seeds persist through the winter [113,165], though dispersal is described as occurring from September to April in both its native (review by [167]) and nonnative [325] ranges.
Black locust seeds may persist in the soil for long periods of time. A Michigan flora states that seeds may survive for more than 88 years in the soil [329]. In a laboratory study, seed from 107 plant species was buried up to 42 inches (107 cm) in soil. Black locust was 1 of 16 plant species with more than 15% of seeds viable after 39 years [316]. Other sources state that seeds remain viable for more than 10 years ([325], review by [26]) or "many" years [87,113]. In mixed-oak and northern hardwood forests of western North Carolina, black locust seeds remained viable in the soil for more than 1 year. Soil seed densities were higher than seed rain, suggesting low annual seed mortality and the presence of seeds from previous years [155].
Because black locust seeds are persistent, they may accumulate to great levels in the seed bank. In Hungary, seeds accumulated over decades in the top 4 inches (10 cm) of soil (review by [181]). In a second-growth mixed-hardwood forest in Great Smoky Mountains National Park, black locust seeds were found in the soil at a density of 29,817 seeds/acre (73,680 seeds/ha) [118]. In contrast, in a mature mixed-oak-maple forest in southwest Virginia, black locust seeds were found at a density of only 121 seeds/acre (300 seeds/ha). The authors suggested that the continuous cover of mature forest would make it difficult for early-successional species like black locust to produce a large quantity of seeds [285].
Black locust seeds are dispersed by gravity (review by [26]), wind ([273,280], review by [26]), and potentially by birds [154,155].
Large size causes most black locust seeds to fall near the parent plant (review by [314]), and black locust is generally considered to have a low dispersal rate [87]. However, long-distance dispersal is possible; black locust recruited by seed onto a revegetating landfill site on Staten Island, New York. The closest seed source was 397 feet (121 m) from the landfill [280].
Establishment: Black locust requires open conditions for establishment ([252,297], reviews by [167,314]). Establishment is often linked to natural ([37,164], review by [167]) and manmade ([99,103,285], review by [167]) disturbances. See Successional Status for more information on this topic.
Growth rate: Black locust is known for its rapid juvenile growth rate ([24,59,126,137,202,291,361], review by [167]). In mixed-oak, cove, and northern hardwood forests in North Carolina, the 5-year average radial growth rate for black locust was 1.31 mm/yr, which was the highest of the 7 species tested [361]. The growth rate of black locust seedlings is limited by plant density ([120], review by [167]) and insect infestations [120,365] and enhanced by light [164], moisture [23,185], and fertilization [23,365].
In its native range, black locust grows rapidly following disturbances such as logging or mining. In regenerating hardwood forests in North Carolina, black locust seedlings grew 26 feet (8 m) in 3 years. They grew faster than any other species for 10 to 20 years [24]. Black locust had the second-tallest mean height of dominant hardwood species 5 years after clearcut treatments in mixed-oak stands in Virginia, with trees as tall as 8.6 feet (2.6 m) [364]. After overstory removal in Pennsylvania mixed-oak stands, black locust seedlings were 3.4 feet (1.0 m) tall 1 year after treatment and 8.1 feet (2.5 m) tall 4 years after treatment [126]. On limestone and acid-shale mine sites in Ohio, direct-seeded black locust reached an average height of 25 feet (8 m) in 7 years, which was higher than any other plant species [202].
Black locust growth rates are also high in its nonnative range. A review states that black locust growth rates in plantations in the central states could average as much as 42 feet (12.8 m) in 10 years, 68 feet (20.7 m) in 25 years, and 84 feet (25.6 m) in 40 years [167]. In experimental old-field rehabilitation plantations in Iowa, 12- to 15-year-old black locust had the highest annual height growth (µ=2.47 feet (0.75 m)) of any species planted [137]. On mine reclamation sites in southeast Kansas, black locust had the fasted growth of all planted species, growing 23 feet (7 m) in 10 years [291].
Density: Black locust may grow at high or low densities depending on local site characteristics. Within its native range, seedling densities are variable. There are often few seedlings under canopies containing mature black locust [172,297]. Black locust seedling density was 125 seedlings/ha in an old-growth mixed-hardwood forest in West Virginia [2]. In contrast, in the Nantahala National Forest in North Carolina, oak-hickory-poplar forest gaps created by clearcutting contained numerous black locust seedlings (3,854 seedlings/ha) and sprouts (2,616 sprouts/ha) 2 years after treatment [297].
Within mature forests of its native range, black locust usually occurs as a canopy tree at low density [1,2,7,40,47,88,92,106,172,205]. For example, there were significantly more black locust stems in 35-year-old, second-growth (22.3 stems/ha) compared to old-growth (4.1 stems/ha) mixed-hardwood forest in eastern Kentucky (P<0.05) [220]. See Successional Status for more information.
In its nonnative range, black locust trees may establish in high densities outside of plantation settings ([231,252], reviews by [72,226]). In a disturbed forest regenerating after a horticultural area was abandoned in New York, black locust established 97 stems/acre (240 stems/ha) in the 8- to 12-inch (20-30 cm) size class and 32 stems/acre (80 stems/ha) in the 12- to 16-inch (30-40 cm) size class in 20 to 40 years. Black locust also dominated the seedling and sapling layer of a mixed-oak dry forest, occurring at a density of 898 stems/acre (2,220 stems/ha) in the 0- to 1-inch (0-2.5 cm) size class [260]. In a pine barrens community near Albany, New York, black locust occurred in nearly pure patches covering 1.2 to 12 acres (0.5-5 ha); these patches were surrounded by pitch pine and scrub oak [231]. In restored oak savanna and woodland sites in Minnesota, black locust stem densities ranged from 4 to 400 stems/acre (10-1,000 stems/ha), with some areas completely dominated by black locust (Kruger personal communication cited in a review [283]).
The scientific name of black locust is Robinia pseudoacacia L. (Fabaceae) [85,91,123,128,143,153,156,178,232,360].
Black locust hybridizes with Kelsey locust (R. kelseyi), New Mexico locust (R. neomexicana), clammy locust (R. viscosa), and bristly locust (R. hispida) (reviews by [167,203]). Several black locust cultivars are available [325].
Vegetative regeneration is important to the establishment, spread, and persistence of black locust. It is thought to be a more common means of reproduction than seed (reviews by [26,131,314]). Black locust commonly sprouts from roots [90,102,133,156,239,258,272,291,306,363] or the stump ([90,102,108,291,306,365], reviews by [72,167,226]). Sprouting often occurs in response to stem or root damage ([90], reviews by [167,226]) due to cutting ([108,306,365], reviews by [72,167]), fire ([108,133], review by [72]), wind, or disease (review by [72]). Root sprouting is also a common means of reproduction following logging treatments [15,363] and a means of spread into revegetating reclamation sites [139] and out of plantations and into abandoned fields [183].
Root sprouting usually begins when plants are 4 to 5 years old (reviews by [131,167]) and increases rapidly in full sun, open areas, and particularly in sandy soils (review by [131]). Though sprouting is a common response to disturbance, sprouts need sufficient light to survive [35].
See Physical and/or mechanical control for more information on how black locust's regenerative abilities impact control efforts.
